This invention relates generally to the field of water purification filters, and more particularly to the field of multiple stage filters having multiple filtering media. Even more particularly, the invention relates to such filters capable of removing microbiological particles and contaminants such as bacteria, cysts and viruses, where the filter is constructed to provide an extremely long useful life before replacement is required.
Drinking water which passes the minimal acceptability standards for contaminants still contains large amounts of impurities and contaminants. These contaminants may include natural and synthetic organics, microorganisms, such as bacteria, viruses, cysts, algae and fungi, suspended inorganic particulates and chemicals. These contaminants negatively alter the taste and odor of water. In instances where filters are employed to remove some of these contaminants, the filter itself can become a breeding ground for the microorganisms. Additionally, as filter media having very small pore size are incorporated to trap contaminants of very small diameter, the problem of pore clogging after extended use increases greatly.
It is known to utilize granulated activated carbon containing silver, multiple stages and membrane type filters to address the problems set forth above. The granulated activated carbon acts to adsorb a majority of the organic and inorganic contaminants, and the silver prevents the growth of bacteria trapped within the filter media. Multiple stage filters allow different filter media to be incorporated into a single filtering device. The different media may filter different types of contaminants using different entrapment mechanisms or they may vary in pore size. Membranes of very small pore size in the submicron range are known, but in current systems utilizing these membranes they tend to clog relatively quickly, leading to loss of water flow and pressure.
Obviously, the less often a filter needs to be replaced due to organic growth or restricted water flow, the more convenient it is to use. In commercial settings, such as for example individual vending machines located at numerous sites, it is very costly to replace the filters since a service technician must service each unit individually. Regulations for commercial vending machines in some instances require as much as a 5 log (99.999%) reduction in the bacteria Streptococcus Faecalis with a flow rate not less than 2 liters per minute at a pressure not to exceed 28 psi. A typical vending machine remains in service for three years before requiring an overhaul, and filters currently meeting the above standards must be replaced many times during the three years due to clogging.
It is an object of this invention to provide a water purification filter which is capable of removing organic and inorganic contaminants of extremely small diameter, down to the submicron range. It is a further object to provide such a filter which overcomes the clogging problem associated with conventional filters such that it has a greatly extended useful life of up to 3 years or the capability of filtering over 30,000 liters without a large reduction in the flow rate. It is a still further object to provide such a filter which is capable of removing viruses in the submicron range as well as over 99.9999 percent of bacteria present in water.